1. Field of the Invention
My invention consists of a wheelchair which provides means whereby the wheelchair may operate over smooth level surfaces and may also be operated to climb or descend stairs.
There is an urgent need for such a structure which can be safely operated by the occupant of the wheelchair and in which the various elements are easy to operate and in which the wheelchair is of relatively simple construction.
I know of no such structure on the market today and I am acquainted with prior art patents found in a patent search, none of these patents, however, disclose anything comparable to my present invention.
2. Description of the Prior Art
The patent to R. W. McKinley issued Dec. 28, 1965, U.S. Pat. No. 3,226,129, discloses a wheelchair with wheels in which the periphery is articulated to lock over the edge of a step and thus provide traction. Stabilization while operating the chair for climbing or descent is provided by a second pair of movable articulated wheels which are described as being positioned to adjust to the stair angle to permit level ascent or descent. The chair has a high center of gravity. Precise adjustments are needed to pass over the edges of the steps. The chair is dangerous, complicated, of excessive weight, and is not a practical nor operative structure.
The patent to G. H. Green issued July 28, 1964, U.S. Pat. No. 3,142,351, discloses a wheelchair propelled by an arbiting walking beam. Stabilizing bars are extended to increase stability. There is no coordinating mechanism to cope with the problem of going over the top of the stairs smoothly. There are over 200 parts described indicating the complexity of the system. The weight of the chair would be considerable. There is danger of damage to stairs from rubbing parts.
The patent to G. D. Grogan issued Apr. 13, 1965, U.S. Pat. No. 3,178,193, discloses a wheelchair based on a complex hydraulic actuated pair of grousers which engage the stair steps and provide traction for moving the chair up the stairs. The weight of the chair is supported on a roller-supported continuous tread which is free wheeling. A hand crank makes angle adjustments of the tread angle for stair angle. The chair has a high center of gravity and a narrow base easily tipped forward. Precise adjustments are needed to descend and it is easily possible to fall backward when getting over the top of the stair.
Other patents known to me which are not of any pertinence whatsoever are listed as follows: U.S. Pats. E. O. Clay, No. 3,049,364, issued Aug. 14, 1962; W. E. Davis, et al., No. 3,054,622, issued Sept. 18, 1962; E. M. Richison, et al., No. 3,133,742, issued May 19, 1964; D. E. Brenner, No. 3,196,970, issued July 27, 1965; and B. M. Bradley, No. 3,438,641, issued Apr. 15, 1969.